Allow specifying the Dockerfile to use

Introduce the DOCKERFILE environment variable which allows to specify
the Dockerfile to use. It is introduced to enable the build and
publishing of development docker images, by using
DOCKERFILE=Dockerfile-dev.

Change-Id: I50fc93d77811123def6b5f86085c35c642c0b011

build_multiplatform.sh

diff --git a/build_multiplatform.sh b/build_multiplatform.sh
index 93a7891..c4ee001 100755
--- a/build_multiplatform.sh
+++ b/build_multiplatform.sh
@@ -3,7 +3,9 @@
 help() {
   echo "Helper script to build single or multiplatform (depending on the input parameter)"
   echo "images for both almalinux and ubuntu distributions."
-  echo
+  echo "DOCKERFILE environment variable points to the name of the Dockerfile to use, which"
+  echo "is Dockerfile by default."
+  echo ""
   echo "Syntax: $0 [--load|--push]"
   echo "options:"
   echo "load     Builds single platform (of runner's system type) images and loads them into"
@@ -15,6 +17,7 @@
   echo
 }
 
+DOCKERFILE=${DOCKERFILE:-Dockerfile}
 DESTINATION=$1
 
 if ! [[ "$DESTINATION" =~ ^(--load|--push)$ ]]; then
@@ -67,11 +70,11 @@
 
 echo
 echo "### Building almalinux multi-platform: [$PLATFORMS] iamges"
-(cd almalinux/10 && docker buildx build --platform "$PLATFORMS" --no-cache -t "$DOCKER_USER:${VERSION}-almalinux10" -t "$DOCKER_USER:$VERSION" "$DESTINATION" .)
+(cd almalinux/10 && docker buildx build -f $DOCKERFILE --platform "$PLATFORMS" --no-cache -t "$DOCKER_USER:${VERSION}-almalinux10" -t "$DOCKER_USER:$VERSION" "$DESTINATION" .)
 
 echo
 echo "### Building ubuntu multi-platform: [$PLATFORMS] iamges"
-(cd ubuntu/26 && docker buildx build --platform "$PLATFORMS" --no-cache -t "$DOCKER_USER:${VERSION}-ubuntu26" "$DESTINATION" .)
+(cd ubuntu/26 && docker buildx build -f $DOCKERFILE --platform "$PLATFORMS" --no-cache -t "$DOCKER_USER:${VERSION}-ubuntu26" "$DESTINATION" .)
 
 echo
 echo "### Removing multi-platform builder"